1. Field of the Invention
The present invention relates to an image processing system, image processing method, and an image processing program product for extracting edge signals from an image signal acquired by an image pickup device.
2. Description of the Related Art
In general, digital image pickup devices such as digital cameras, digital video cameras, etc., comprise an image pickup device, an analog circuit which performs various kinds of analog processing for an analog signal outputted from the image pickup device, and an A/D converter which converts the signal outputted from the analog circuit into a digital signal.
In general, digital signals thus outputted from the A/D converter of such a digital image pickup device contain various noise components. With conventional techniques, in order to extract an edge signal from the image signal with such noise components, predetermined processing, i.e., so-called coring processing, is performed, thereby suppressing the adverse effects of such noise components.
Examples of such techniques include a technique disclosed in Japanese Unexamined Patent Application Publication No. 8-107565, in which edge components are extracted for each of the R, G, and B signals so as to perform the coring processing using predetermined noise identification reference values. Such an arrangement reduces the adverse effects of thermal noise, thereby allowing the edge components to be extracted with high precision.
Also, Japanese Unexamined Patent Application Publication No. 9-121366 discloses a technique in which determination is made whether or not the edge signal is noise based upon the correlation between the R, G, and B signals and the amplitude of the edge signal. In a case in which determination has been made that the edge signal is noise, the coring processing is performed. Such a technique suppresses the adverse effects of noise among these color signals, thereby allowing the edge components to be extracted with high precision.
Also, Japanese Unexamined Patent Application Publication No. 2005-130297 discloses a technique in which the noise component is dynamically estimated based upon the image signal so as to dynamically control the coring processing. Such an arrangement enables the edge component to be extracted with high precision regardless of dynamic fluctuation of the noise component.
Also, Japanese Unexamined Patent Application Publication No. 2005-175718 discloses a technique in which dynamic estimation of the amount of noise is performed with respect to the luminance signal and the color difference signal so as to perform high-quality noise reduction processing.
In the aforementioned technique disclosed in Japanese Unexamined Patent Application Publication No. 8-107565, the noise identification reference values are provided in the form of static values. However, the noise arising due to the image pickup device can dynamically fluctuate due to various factors such as the image signal level, the gain thereof, the temperature of the image pickup device when the image is acquired, etc. Accordingly, such a technique disclosed in this patent application Publication does not have a function of performing optimum noise estimation giving consideration to such dynamic fluctuations of these factors. In some cases, this leads to reduction in the precision of the coring processing results. Also, in the aforementioned technique disclosed in this Patent Application Publication, the edge signal is corrected based upon the noise components. However, the nature of the noise component differs from that of the edge signal. Accordingly, such a technique does not ensure high-precision correction.
In the aforementioned technique disclosed in Japanese Unexamined Patent Application Publication No. 9-121366, noise identification is performed based upon the correlation between the color signals. Accordingly, in a case in which there is little correlation between color signals in the subject image, e.g., in a case in which image pickup is performed for a subject that is almost a single color image, such a technique provides coring processing with reduced precision. This leads to a reduction in the precision of the edge component extraction. Also, in the technique disclosed in this patent application Publication, the edge signal is corrected based upon the noise components. Accordingly, for the above-described reason, such a technique has a problem of poor correction precision.
Also, in the aforementioned technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-130297, the edge signal is corrected based upon the noise components. Therefore, for the above-described reason, such a technique also has a problem of poor correction precision.
On the other hand, the purpose of the aforementioned technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-175718 is not to extract the edge components with high precision. However, this Patent Application Publication discloses a technique in which the noise reduction processing and the edge extraction processing are performed as mutually independent processes. Accordingly, such a technique has a problem of performing the noise reduction processing and the edge extraction processing without mutual cooperation.
The present invention has been made in view of the aforementioned problems. Accordingly, it is an object thereof to provide an image processing system, image processing method, and an image processing program product which provide a function of performing stable extraction of the edge components with high precision even if the image signal contains various kinds of noise.
Furthermore, it is another object of the present invention to provide a low-cost image processing system, image processing method, and image processing program product which are capable of acquiring high-quality image signals.